Various techniques are available for determining the relative position of a control rod within a nuclear reactor. Such techniques can utilize ultrasonic methods or magnetic approaches for determining the position of the control rod. Magnetic approaches typically depend upon the magnetic structure of the control rod, or the inductive coupling between the control rod and the magnetic windings of the measuring device, or the change in magnetic flux resulting from control rod movement. Such approaches are directed to detecting the relative position of a single control rod rather than to comparing the relative position of the control rods within a group. The comparison of the relative position of the control rods within a group can reveal the existence of an alarm or fault condition.
Because of the foregoing, it has become desirable to develop a method for comparing the relative position of control rods within a control rod group to determine if an alarm or fault condition exists within the nuclear reactor.